Process and apparatus for fiber bundle impregnation

ABSTRACT

The invention relates to a fibre bundle impregnating process, in which the fibre bundle is placed on a support and the support, together with the fibre bundle thereon, is moved past an impregnating device. In this process the fibre bundle is supported during the impregnation process and consequently a fibre-reinforced plastic is produced, fibre breaks being largely avoided during its production. One of the possible variants of the inventive concept comprises an impregnating wheel, which receives the fibre bundle and leads it past an impregnating device.

This is a national stage application of PCT/EP 95/01476, filed Apr. 19,1995.

BACKGROUND OF THE INVENTION

Field of the Invention

Discussion of the Background

Such a process is known from EP 415 517 B1. This document describes aprocedure with a one-sided impregnating direction, in which an elevatedsystem pressure of the liquid matrix material is built up at rightangles to the fibre bundle. The fibre bundle is drawn via a nozzle headand the matrix material is forced through at right angles to the bundlemovement direction. In this process the tribological stressing of thefibre bundle is high and the quality of the material produced can bereduced by a plurality of individual filament breaks in the fibrebundle. The filaments in a fibre bundle are often in the form ofaccumulations, i.e. not uniformly distributed over the fibre bundlecross-sectional surface.

As a result of this non-uniform distribution the flowing matrix meltsplits the fibre bundle and consequently the matrix flows through thegap and not through the fibre bundle to be impregnated. However, evenwithout the splitting of the fibre bundle the matrix always attempts tofollow the path of least resistance, i.e. it only penetrates the fibrebundle where the thickness of the latter is at a minimum. This meansthat points having a large number of superimposed filament layers areinadequately impregnated.

Problems during impregnation are the high viscosities of the matrixmaterials and the high break sensitivity of the individual filamentswithin the fibre bundle. The individual filaments are very closetogether and it is difficult to uniformly impregnate all round thefilaments with the matrix material. It is also necessary to ensure thatwithin the impregnated fibre bundle, also known as a tape, no airinclusions or inadequately wetted zones are formed, which greatly reducethe strength, stiffness and other mechanical characteristics of thefibre bundle.

SUMMARY OF THE INVENTION

The object of the invention is to provide a process of theaforementioned type, in which there is a particularly good impregnationof the fibre bundle or some other fibre preform (e.g. fibre mats) in thecase of a high throughput and at the same time filament breaks can belargely prevented. In addition, an apparatus is to be provided forperforming the process according to the invention.

According to the basic concept of the invention the fibre bundle iscarried along on a support during the impregnating process. The fibrebundle is supported by the support and led past the impregnating device.Thus, there is no relative movement between the fibre bundle and fixedparts of the impregnating device. Thus, abrasion processes, a hightribological stressing of the fibre bundle and also the impregnatingtool are avoided. As a result of the supporting action of the support,the fibre bundle is effectively relieved, even in the case of a highimpregnating pressure. As a result of the use of a support filamentbreaks are largely avoided and consequently the quality of theimpregnated fibre bundle is improved.

In an advantageous further development the fibre bundle is secured onthe support by additional measures. This leads to a particularly goodcontact between the bearing surface and the fibre bundle, so that thefibre bundle is particularly well protected against compressive loadingduring the impregnating process. This can be achieved by simplytensioning the fibre bundle, e.g. by guiding said bundle over a brakedroll.

Matrix material is supplied to the fibre bundle in the following way.With the aid of a pressure built up in the feed mechanism (extruder), inthe liquid state the matrix material is forced through a permeablebearing surface and then further guided through the fibre bundle. It isalso possible to have a matrix material supply from the other side, i.e.initially through the fibre bundle and then through the support,provided that no use is made of the described uniform through-flowprinciple. In both cases the support fulfils its supporting function.

For reducing the pressure it is advantageous for the impregnatingprocess to take place over a maximum large area. Then the impregnationcan be performed with limited pressure and a constant quality andconsequently a fibre-reinforced plastic with very few filament breaks isproduced.

The main advantages of this process are that the fibre bundle is notsubject to abrasion during the impregnating process as a result ofrelative movements between the fibre bundle and the impregnatingstation, because according to the invention virtually all relativemovements between filaments of the fibre bundle and components of theimpregnating station are avoided. It is possible to regulate within wideranges the volume percentage of fibre to matrix material. It is alsopossible in this process to achieve a very high discharge quantity andkeep the matrix overflow to a very low level. As a result of thedescribed construction of the support, a complete impregnation, even inthe case of non-uniform filament distribution over the fibre bundlewidth is ensured.

In a particularly advantageous development of the invention use is madeof an impregnating wheel as the support. In the case of an impregnatingwheel with a fixed hub only the contact surface or tread is rotatableand made permeable for the liquid matrix material. As the contactsurface rotates with the drawing-off speed of the fibre bundle, there isno relative movement between the substrate and the fibre bundle. Thereis no filament rubbing against fixed machine parts and filament breakscaused by abrasion cannot arise.

The impregnating device and further means for performing the process canbe positioned in the vicinity of the fixed wheel hub. The impregnatingarea widened with respect to a small nozzle permits a lower impregnatingpressure. The fibres are not subject to a pressure surge, as occurs withan impregnating nozzle and instead are gently impregnated until thedesired degree of impregnation is reached at the end of the impregnatingarea. The throughput can be randomly increased by the time extension ofthe impregnating process, i.e. the impregnating time, which can bebrought about by increasing the impregnating wheel diameter.

A further throughput increase is achieved in that several fibre bundlesare guided in juxtaposed manner, i.e. in parallel on the impregnatingwheel and simultaneously the width of the latter is made appropriate forseveral juxtaposed bundles. The throughput can once again be increasedat random.

The path of the liquid matrix from the interior of the impregnating toolup to the fibre bundle, i.e. the residence time of the molten matrix insaid tool is short. This means that the risk that due to a longthermostatic control of the matrix could lead to damage, e.g. in theform of thermal deterioration is limited. Due to the open constructionrapid access to all components is possible and the setting-up time iscorrespondingly short.

In a further development of the invention the fibre bundles are heatedprior to impregnation, e.g. this can take place by hot air. Theseparation of the impregnated fibre bundle can also be improved by theinflow of thermostatically controlled air, which is under elevatedpressure.

In another further development, several impregnating wheels can besuccessively arranged and can contrarotate. This can be advantageous insome cases and can also lead to a further throughput rise due to fasterdrawing-off speeds for the fibre bundles.

In another further development in the vicinity of the support, which isnot covered by the fibre bundle, is fitted a contact surface cleaningdevice. Thus, there is always a well prepared contact surface forreceiving the fibre bundle and which has virtually no matrix residues.

In other embodiments the support can e.g. comprise a rotating belt orrotating chain links or also a bearing surface with a return mechanism.

Frequently used fibre materials are glass, carbon or aramide fibres.Standard matrix materials are thermosetting and thermoplastic materials.However, the process according to the invention is not restricted tothese materials and instead numerous materials can be used in theproduction of fibre-reinforced materials.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter relative to theattached drawings, wherein show:

FIG. 1 A diagrammatically represented overall construction of anapparatus according to the invention.

FIG. 2 A diagrammatic view of an impregnating wheel in side view.

FIG. 3 A diagrammatic sectional representation of an impregnating wheel.

FIG. 4 A diagrammatic representation of a rotary impregnating belt.

FIG. 5 A diagrammatic representation of a support with return mechanism.

FIG. 6 A diagrammatic representation of the flow through a homogeneousbody.

FIG. 7 A diagrammatic representation of the flow through a permeablesupport.

FIG. 8 A diagrammatic, part sectional view of an impregnating wheel witha larger scale detail.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a diagrammatic overall construction of an apparatusaccording to the invention. If necessary, the impregnating processbegins with the merging of small fibre bundles, which are supplied fromholders 1. The number of small fibre bundles required is a function ofthe desired strength and thickness of the finished fibre bundle. FIG. 1shows three small fibre bundles 6a, 6b and 6c. The merged fibre bundle 6can be brought to the necessary tensile stress by deflecting the fibrebundle by means of a braked roll 2.

At this point starts the action zone of the impregnating stationaccording to the invention and which in FIG. 1 is constructed as animpregnating wheel 3. Following the actual impregnating process ashaping device 4 can be rendered available for the subsequent shaping ofthe fibre bundle, so that it can then be rolled onto a roll 5 as afinished, impregnated fibre bundle. Immediately after leaving theimpregnating wheel, the impregnated fibre bundle can also undergofurther processing.

FIG. 2 shows diagrammatically the operation of the impregnating wheel.The fibre bundle 6 runs over the contact surface 35 rotating at the samespeed, whereas the hub area is fixed. The first area 31 is used forheating the incoming fibre bundle, where heated air flows through thecontact surface at the fibre bundle. The actual impregnating processtakes place in the second area 32, where the liquid matrix material isforced at an elevated pressure through the contact surface and the fibrebundle to be impregnated until the desired degree of impregnation isreached at the end of the area. As the impregnating process takes placeover a large angular range, there must be an adequate impregnating timefor complete impregnation. Thus, the necessary matrix pressure, whichacts vertically against the fibre bundle, can be kept as low aspossible. A low internal pressure also reduces the necessary fibrebundle tension. The throughput can be increased by means of an increasedrotary speed of the contact surface 35. In the third area 33 theimpregnated fibre bundle is separated from the contact surface 35. Thefibre bundle can leave the contact surface 35 with thermostaticallycontrolled air, elevated pressure and through the given drawing-offdirection. In the final area 34 there is no fibre bundle on the contactsurface 35, which can once again be prepared for receiving the fibrebundle. The individual areas are also to be understood as closedchambers, whose walls are firstly constituted by the shaped areas of thefixed hub and secondly by the contact surface rotating at the fibrebundle speed. The necessary media are supplied from the outside into thechambers by connecting pieces.

FIG. 3 shows the impregnating wheel in plan view. The contact surface 35is permeable for the liquid matrix material and rotatable. The contactsurface width corresponds to that of the fibre bundle obtained. Themarginal areas are raised somewhat. Heated air is passed into the area31 through the supply device 31a. The supply device 32a passes theliquid matrix material to the impregnating device. Thermostaticallycontrolled air at an elevated pressure is passed through the supplydevice 33a into the area 33.

FIG. 4 shows another embodiment of the invention. A rotating belt 45,which can also be built up from chain links, runs over two or more rolls41. The fibre bundle 6 is received from the revolving belt 45 and ledpast the impregnating device 42. In the presently shown embodiment thematrix material is pressed from above, i.e. initially through the fibrebundle and then through the bearing surface. Here again it isadvantageous if the bearing surface is permeable for the matrixmaterial.

In FIG. 5 the fibre bundle 6 is led with a support 55 past theimpregnating device 42. The support 55 initially moves at the speed ofthe fibre bundle 6 and is then moved initially downwards by a returndevice 56 and then at high speed back to the starting position. Througha skilled control of the return device 56, in conjunction with a timeand/or space control of the impregnating device 42, it is possible toensure that each part of the fibre bundle is uniformly impregnatedwhilst being supported from below.

FIG. 6 generally shows how fluids can flow through a homogeneous body. Ahomogeneous body 60 is shown through which a fluid flows from below. Thearrows 62 indicate the flow direction and correspond to the impregnatingdevice supplying a matrix material. The arrows 61 indicate that thefluid passes uniformly out of the exit surface of the homogeneous body60, because the latter has a homogeneous penetration resistance over itsentire volume.

With reference to FIG. 7 the significance of the principle of theuniform through-flow in the case of fibre bundle impregnation isdescribed. A fibre bundle 6, unwound from a roving or a holder 1,comprises a large number of fibres, which can also be called filaments.On closer consideration of a fibre bundle 6, it can be seen that thefilaments are not uniformly juxtaposed and superimposed over the width.There are areas 64 in which the filament planes are accumulated. Thesefilament accumulations 69 are located along a fibre bundle at differentpoints of the cross-sectional surface. For impregnation this means thatthe penetration resistance of a fibre bundle is not constant for themolten matrix material over the cross-section thereof. In filamentaccumulation areas the penetration resistance is high, whereas it isonly low in areas consisting solely of a few filament planes. It is alsopossible for the matrix material to split the fibre bundle 6 onpenetrating at a thin point 63 and then a large part of the matrixmaterial flows through this gap in the fibre bundle 6 and consequentlythe pressure built up in the matrix material drops. Therefore there canbe no impregnation at points with filament accumulations 64. As thefilament distribution of a fibre bundle 6 can only be levelled out to acertain extent, the structure described with reference to FIGS. 7 and 8offers a good possibility for ensuring a high degree of impregnationindependently of the thickness distribution of the filament planes. Acorrespondingly designed support has its own inventive character.

This case is illustrated in FIG. 7. The fibre bundle 6 to be impregnatedis firmly connected to a homogeneous, porous body 65, which can be partof the support and is constructed for receiving the fibre bundle and ispermeable for the liquid matrix material. If said body 65 is firmlyconnected to the fibre bundle 6 to be impregnated, whose impregnationresistance is clearly lower and distributed in a non-uniform manner,then the flow through the fibre bundle takes place with a uniform flowfront. This is due to the fact that in said fibre bundle 6 the matrixmaterial can enter with a constant pressure and under constant flowspeed conditions. The flow front flows uniformly through the fibrebundle 6, provided that the latter is not too thick compared with thethickness of the homogeneous body 65. The body 65 or that part of thesupport which receives the fibre bundle 6, must consequently have aconstant penetration resistance, which is higher than that of the fibrebundle to be impregnated. Therefore there is a flow through the fibrebundle 6 in the radial direction with a continuous uniform matrixmaterial flow front, which is independent of the filament distributionof the fibre bundle. This is brought about in that the body 6 isconstructed as a cylinder portion with a high penetration resistance.

FIG. 8 shows the flow through the fibre bundle described in FIGS. 6 and7 on an impregnating wheel described relative to FIG. 2. The contactsurface 35 of the impregnating wheel is formed from a homogeneous layerof a material with a high penetration resistance. The contact surface 35is traversed from the inside by the liquid matrix material and this isgiven the reference numeral 68 in the larger scale detail. As a resultof this construction of the contact surface 35 there is a uniform flowfront, so that there is a uniform flow through the outer fibre bundle 6.This takes place independently of whether the fibre bundle 6 has auniform or a non-uniform thickness distribution.

I claim:
 1. A process for fiber bundle impregnation, comprising thesteps of:placing a fiber bundle on a support, wherein said support is awheel having a fixed hub region and a rotary contact surface whichcontacts the fiber bundle; passing said rotary contact surface havingthe fiber bundle thereon past a matrix material impregnating device; andimpregnating said fiber bundle with said matrix material from theimpregnating device, wherein there is no relative movement between therotary contact surface and the fiber bundle during said impregnatingstep.
 2. The process of claim 1, wherein a tensile stress is exerted onsaid fiber bundle during said process.
 3. The process of claim 1,wherein said fiber bundle is heated prior to said impregnating step. 4.The process of claim 1, wherein said matrix material passes through saidrotary contact surface to said fiber bundle.
 5. An apparatus for fiberbundle impregnation, comprising:a movable support for receiving a fiberbundle, wherein said support is a wheel having a fixed hub region and arotary contact surface which contacts the fiber bundle; and animpregnating device for impregnating the fiber bundle with a matrixmaterial, wherein said movable support is located in an area for passingmatrix material through said rotary contact surface to said fiber bundlefrom said impregnating device, and wherein said support is adapted suchthat there is no relative movement between the rotary contact surfaceand the fiber bundle during impregnating.
 6. The apparatus of claim 5,wherein said support is adapted for receiving and impregnating aplurality of parallel fiber bundles.
 7. The apparatus of claim 5,comprising a plurality of supports arranged in succession, wherein therotary contact surfaces of said supports move in opposition to oneanother so as to permit impregnation from opposing sides of a fiberbundle.
 8. The apparatus of claim 5, wherein said surface is permeableto said matrix material, said surface is homogeneously constructed sothat there is a constant penetration resistance for said matrixmaterial, said surface has a higher penetration resistance for saidmatrix material than the penetration resistance of the fiber bundle.